You shroud a single trap with a powerful illusion to make it more difficult to locate. Spells like detect magic can’t locate any magic aura from either the target trap or from undetectable trap. Furthermore, a character under the effect of the find traps spell doesn’t receive an automatic chance to locate the target trap when she comes within 10 feet of it, and the bonus on Perception checks from find traps doesn’t apply to attempts to notice the target trap. Add 1/2 your caster level to the DC for any creature without the trapfinding class ability to notice the target trap with Perception checks.

A ranger with the ranger traps class feature can cast this spell on a ranger trap he creates as part of the same action he uses to prepare a ranger trap. This doesn’t reduce the spell’s casting time if such a ranger casts this spell on an ordinary trap, even one that he created himself using Craft (traps).